(1) Field of the Invention
This invention relates to a method for recovering liquid polymers. More particularly, the invention relates to a method for recovering low molecular weight polymers that contain no catalyst residue, in which conjugated diolefins are polymerized or conjugated diolefins and vinyl compounds having anionic polymerization activity are copolymerized in the presence of a catalyst mainly containing organic sodium compounds, and the obtained liquid polymerization mixture is then uniformly mixed with an aqueous solution of isopropyl alcohol to decompose the catalyst and to transfer catalyst residue into the isopropyl alcohol aqueous solution, thereby separating and recovering the low molecular weight polymers.
Further, in the method of the present invention, liquid low molecular weight polymers of conjugated diolefins are prepared in the presence of a catalyst mainly containing organic sodium compounds in a polymerization inert solvent and the obtained polymerization mixture is then combined with a certain quantity of an aqueous solution of isopropyl alcohol at a certain concentration. The catalyst component in the polymerization mixture is decomposed and the catalyst residue is transferred into the aqueous solution of isopropyl alcohol. Therefore, the liquid low molecular weight polymers containing substantially no catalyst residue can be obtained.
(2) Description of Prior Art
Liquid low molecular weight polymers that are prepared by polymerizing or copolymerizing conjugated dienes such as butadiene and isoprene, have many unsaturated bonds in their molecules, so that they are widely used for producing thermosetting resins, drying oils, sealing materials, water-soluble coating materials, electrodeposition coating materials, electric insulators, rubber modifiers and various kinds of reactive intermediates. Accordingly, it is desirable that the liquid low molecular weight polymers of conjugated dienes as raw materials do not contain catalyst residues at all because undesirable influences in secondary chemical reactions and lowering of the properties of final products occur when the catalyst residue is contained.
It is well known in the art that a liquid low molecular weight polymer is prepared by polymerizing or copolymerizing butadiene or butadiene and another monomer in the presence of alkali metal or its organic compound such as alkyl sodium. (For example, U.S. Pat. No. 3,789,090).
The liquid polymerization mixture obtained from the above reaction contains the alkali metal or its organic compound in dispersed state or dissolved state. Several methods have been proposed to decompose and remove catalyst components out of the polymer.
In the method described in U.S. Pat. No. 2,813,136, a large quantity of hot water is added to a liquid polymerization mixture to decompose and separate catalyst. With this method, however, the catalyst residue cannot be completely removed since an indestructible emulsion is formed. In a method to avoid the formation of emulsion disclosed in Japanese Patent Publication No. 4098 of 1958, the polymerization product is treated with clay containing 1 to 25% of bound water and the resultant mixture is subjected to percolation or filtration. In the method disclosed in Japanese Patent Publication No. 7942 of 1956, hydrogensulfate is produced by using concentrated sulfuric acid and it is then filtered off. In both the methods, it is necessary to remove very fine and considerable quantity of decomposition products of catalysts by means of filtration or centrifugal separation. However, the filter medium is liable to be blocked when a filter is used and in the case of centrifugal separation, continuous operation is difficult. Accordingly, the conventional methods are disadvantageous in that the complete removal of catalyst residue is hard to attain and the loss of obtained polymer is not negligible.
As described above, it is very difficult to decompose the catalyst and to remove it from the polymer solution simultaneously in a single step. In the method disclosed in Japanese Patent Publications, No. 12306 of 1965 and No. 17914 of 1965, the polymer solution is treated with a small quantity of water or dilute acid to form solid decomposition product of catalyst and it is separated by filtration or centrifugal separation in the first step, and in the second step, the separated polymer solution is brought into contact with clay or acid clay so as to remove the remaining decomposition product of catalyst. The decomposition product of catalyst formed in the first step is, however, very fine and sticky so that the filtration is very difficult and the filterable volume per unit area of filter medium is small since the filter medium is liable to be blocked in a short time. Further, in the centrifugal separation, it is also disadvantageous in that continuous treatment is impossible. In addition, the loss of polymer cannot be avoided in both the filtration and centrifugal separation.
In the method disclosed in Japanese Patent Publication No. 40866 of 1972, the catalyst is decomposed and simultaneously separated by adding 4 to 10-fold molar quantity of methanol to the catalyst of alkali metal or its organic compound in the first step and the lower methanol phase containing most of the catalyst residue is then separated and removed. The upper polymer liquid phase is then treated with an absorbent such as clay or alumina to eliminate the contained catalyst residue by adsorption. Since most of the catalyst is separated by decomposing and liquefying the catalyst, the first step of this method is somewhat advantageous as compared with the method of Japanese Patent Publications, No. 12306 of 1965 and No. 17914 of 1965, however, solid industrial waste is produced in the filtration or centrifugal separation after the adsorption of catalyst residue with clay or the like in the second step and this step is accompanied by the loss of obtained polymer. Accordingly, the defect of this method is substantially the same as that of the foregoing method, and this method cannot be either adopted in industrial production.